How to Caulk a Basement Cinder Block

Clear out the space requiring caulking with a wire brush. Scrub the brush over the surface of the cinder block to remove any debris, and then run the brush through the empty space needing filling to remove any debris or dirt buildup inside.

Wash the area with a concrete cleaner and a scrub brush to remove any dirt present. The dirt, if left in place, could interfere with the caulk adhesion. Rinse the area clear with clean water, and then allow the block to dry completely. Drying times will vary but should be no more than two or three hours.

Place a tube of urethane caulk into a caulk gun. Press the trigger of the gun a few times to move the plate of the gun against the rear of the tube. Cut the tip from the tube at a 45-degree angle with a utility knife. Make the cut at a position on the tube that’s about the same diameter as the width of the opening that requires the filling.

Press the tip of the caulking gun against the opening of the crack at its top. Fill the space with the concrete caulk, moving the gun as you do so down the opening until you reach its base.

Smooth the caulk and press it further into the crack with the rounded base of a spoon. Wait the length of time suggested by the caulk manufacturer for the material to dry, and then check the surface for any spaces missed. Apply additional caulk to those spaces if needed.